The present invention relates to measuring flow of process fluid in industrial processes. More specifically, the present invention relates to measuring flow using an averaging pitot tube using differential pressure.
The process industry employs process variable transmitters to monitor process variables associated with substances such as solids, slurries, liquids, vapors, and gases in chemical, pulp, petroleum, pharmaceutical, food and other processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. A process flow transmitter provides an output related to a sensed process fluid flow. The flow transmitter output can be communicated over a process control loop to a control room, or the output can be communicated to another process device such that operation of the process can be monitored and controlled.
Measuring the rate of fluid flow in a confined conduit by modifying the internal geometry of the conduit and applying an algorithm to the measured differential pressure in the flowing fluid, is known. The geometry of the conduit is traditionally changed by altering the cross section of the conduit, such as with a venturi meter, or by the insertion into the conduit of a flow altering device such as a orifice plate, an averaging pitot tube or the like.
An averaging pitot tube generally includes a body that slightly impedes fluid flow within the conduit. A pressure difference between the upstream side and the downstream side of the pitot tube is measured and correlated to flow rate. However, variations in the differential pressure may cause inaccuracies in the flow rate determination.